Lesson 1: Susceptibility

As discussed in a previous lesson, the wear and tear on people’s regulatory systems can make them more vulnerable or susceptible to changes in their environment. Meaning that their risk of impact can be higher than what an average value might present.

Our definition of susceptibility is: the effects of biological inequity on the human immune response, specifically the fact that persistent environmental stressors on a community place these individuals at a heightened risk of developing severe symptoms and chronic illnesses compared to a normative population, not exposed to significant stressors.

An example epidemiological study on this was conducted by Saez and Lopez-Casasnovas (2019) who presented a comparative study on susceptibility between a deprived vs wealthy neighbourhood in Barcelona to pollution. The results indicated that the deprived neighbourhood was significantly more at risk of dying (30% higher probability) from environmental health hazards, such as air and noise pollution, than the wealthy neighbourhood.

This increased susceptibility was due to a mixture of psychosocial stressors that the deprived neighbourhood was experiencing: low income and poverty, low quality of housing and low access to services.

Another study (Rosa et al., 2019) showed compelling evidence of a relationship between prenatal stress and onset of asthma in children. Children born to mothers who experienced high psychosocial stress (eg. divorce, health concerns etc), were significantly more at risk of developing asthma later on in life; the risk further increased when the mothers were also exposed to higher air pollution levels (Rosa et al., 2019).

Expanding on this, Landeo-Gutierrez et al. (2019) argue that certain types of psychosocial stressors, such as exposure to violence and crime, increased the risk of onset of asthma, especially when in co-presence with air pollution. In particular, they found a strong correlation between post-traumatic stress disorder (PTSD) and asthma onset.

At the crux of this theory is that when the body is faced with stressors it adapts through a process called allostasis, which means “achieving stability/homeostasis through change”.

Chronic HPA-axis activation due to constant psychosocial (financial insecurity) and environmental stressors (air pollution), combined with maladaptive behaviours such as poor sleep due to shift work, can impede the allostatic process. This creates ‘allostatic load’, which is “wear and tear” on biological systems that communicate with the stress response, resulting in increased systemic inflammation, and compromised immune and metabolic systems. In the long run, this can leave people more susceptible to the health risks of environmental toxins like air pollution.  

It is also important to note that related to susceptibility is biological degradation. Through the stress response pathways long term exposure to air pollution can have far reaching microbiological effects, which in turn make people more physiologically susceptible to the effects of air pollution. There is growing evidence suggesting that stress may alter permeability of bodily membranes to chemical exposures, such that stress may “alter systemic transport and chemical uptake into organs including the brain, facilitating combined and synergistic effects of stressors and air pollution on many bodily”. 

VARIABILITY 

It must be noted, however, that not all people living in a deprived environment and continuously exposed to stressors, will develop disorders and severe symptoms: even within a vulnerable population there is variability in the outcome of exposure to stressors. This variability is often overlooked by health authorities, leading to average measures being reported within a vulnerable community, and inappropriate guidelines being detailed.

Individuals who suffer from one condition often also suffer from other conditions. When at least two conditions co-occur, we speak of comorbidities. Co-occurring conditions or illnesses can be physical/physical, physical/mental, and mental/mental.

There are different reasons for why conditions co-occur: either the conditions share a common cause, or one condition predisposes the individual for the other condition(s) (source). In any case, it means that very often individuals suffer from more than one condition, meaning that there is even more strain on their health and well-being and that their own and their family’s lives are even more affected. For example, an individual with obesity (a physical condition) may also suffer from cardiovascular disease (a physical disease) and depression (a mental disorder).

Healthy environments are crucial for individual, community, and population health. Being able to live in a healthy house/flat, in a healthy neighbourhood, and in a healthy city is important for people to have the opportunity to achieve optimal health.

A healthy individual should not become sick from living in an unhealthy environment. Equally, an individual who already suffers from a health condition/multiple health conditions should not become sicker just because of where they live. Our environments should help us maintain and improve our health and well-being. Therefore, urban regeneration must put people first and focus on health. It is time to reframe our understanding of regeneration.